Vented fireplaces come in three vent types: conventional, power and direct.
Conventional woodburning fireplaces have been used in homes throughout the years. Although these fireplaces are not usually the primary heating source in todays homes, such fireplaces remain quite popular due to their aesthetic value and charm. Conventional venting of woodburning fireplaces, of course, require some type of chimney for venting the combustion products. As will be appreciated by those skilled in the art, conventional fireplaces are typically built with an outside masonry chimney. Prefabricated woodburning fireplaces typically have metal chimneys that are installed in the outside chimney chase. In newer construction, these chimneys are often framed, and thereafter covered by siding.
Power vented fireplaces exhaust flue products using a power driven blower. They are particularly useful on horizontal or off-vertical runs where it is necessary to supplement the natural buoyancy of the flue products. The decrease in lift from the exhaust on a horizontal run can make it difficult to vent products of combustion.
In recent years, there has been a trend towards the installation of gas fireplaces. These gas fireplaces typically burn cleaner, can be turned on and off with the push of a button, eliminate the need for buying, chopping and storing wood and require little or no maintenance and/or cleaning. Such gas fireplaces were originally installed in similar fashion to conventional woodburning fireplaces, i.e., they were typically installed in the outside chases. However, newer gas fireplace technology allows the fireplace the be moved into the room, rather than being enclosed in an outside chimney chase. The newer fireplaces include both direct vent and vent free models.
Gas fireplaces of conventional design typically utilize a source of combustion air from the room being heated. This lowers the efficiency of the gas fireplace because a portion of the heated air in the room is drawn into the combustion chamber and exhausted up the chimney. It is known to provide separate ducting from the outside ambient environment to the combustion chamber to increase the efficiency of the fireplace. The ducted air provides a source of oxygen for combustion in the combustion chamber and decreases the amount of air from the room being heated which is exhausted up the chimney. Such ducting, however, requires additional materials and labor to install.
Fireplaces which burn gas and which utilize artificial log assemblies to simulate the appearance of burning wood logs are well known in the art. The artificial log assemblies typically include several artificial logs of a ceramic or other refractory material designed to simulate the appearance of wood logs. A gas burner supplies a flammable gas underneath the artificial logs. The gas is burned to produce a flame in the vicinity of the logs. The fireplace can include a tank or reservoir for holding the flammable gas or can be connected to a remote gas source. Fireplaces utilizing artificial log assemblies provide heat and the pleasing appearance of a wood fire, while avoiding the inconvenience and lace of cleanliness associated with the loading of wood into and removal of ashes from conventional wood burning fireplaces.
One objective in the design and construction of gas log fireplaces is to provide artificial logs that look like real logs and to provide gas flames which closely simulate the flames produced by burning wood so that an overall effect of burning wood is produced. Both the size and color of the flame and its position relative to the artificial logs are important in producing a realistic effect.
Other important objectives in the design and construction of gas log fireplaces include providing high heat output, providing high combustion efficiency, minimizing the soot and noxious gases produced by combustion and minimizing the cost of the fireplace.
Direct vent fireplaces have become popular as they do not affect or compromise the indoor air quality and are ideally suited for today's energy efficient, tightly constructed homes and come in a variety of designs, sizes and heat output. Also they must be in compliance with local and national safety standards, the EPA and the American National Standards Institute (ANSI).
A typical direct vent fireplace uses a two duct system which achieves the aforesaid objectives of gas log fireplaces. Combustion air is drawn from the outside of a dwelling through one duct, while the exhaust gases are vented through the other duct. This overcomes much of the problem of drawing air for combustion from within the house and allows for vertical and horizontal runs within limits specific to the fireplace specifications without the use of a fan. Such fireplaces are disclosed, e.g., in U.S. Pat. No. 4,793,322 (Shimek et al.) and U.S. Pat. No. 4,909,227 (Rieger).
Most modern direct vent type gas fireplaces are pre-fabricated units. The basic types are zero clearance, insert, free-standing and wall mount. A zero clearance fireplace, as its name suggests, can be placed against combustible materials. An insert is a unit made to fit within an existing solid fuel burning fireplace, and may use the existing chimney. A free-standing unit may be placed on the floor in a room without support from the wall and may be spaced a distance from the wall. A wall mount is placed on and supported by a wall in the room.
Room air flows by convection, or with the use of a fan, through a passage between the bottom of the firebox and the bottom of the unit, around the rear and sides of the firebox, and out across the top of the firebox directing heat into the room. In order to increase the efficiency of the unit, some manufacturers place a heat exchanger for top vented units in-line with the exhaust outlet over the top of the firebox in the circulating air passage. The heat exchanger impedes the flow of the exhaust gases and provides additional heat transfer surface area which allows for additional heating of the room air.
Some would consider it's not a fireplace without a mantel. It has been recognized that the flow of heated air which exits from the top of a direct vent fireplace can reach temperatures of 400° C. or higher. Accordingly, the use, size and placement of a mantel is a critical safety concern. Although mantels may be of a variety of materials, wood is usually the choice to be coordinated with room decor. Being combustible, builders and installers are advised against placing the mantel contiguous to the front face of a direct vent fireplace. An installation manual for one direct vent appliance depicts how the vertical installation clearances for combustible mantels varies according the depth of the mantel. For example, a mantel 10″ (254 mm) deep is recommended to be placed 12″ (305 mm) vertically above the top of the fireplace. Some mantel installations are being placed even higher, e.g., 16″–17″ to escape soot blackening, charring, or even combustion of the mantel from the elevated heat as it rises from the fireplace. Direct vent fireplaces are uniquely suited for installations requiring utility shelves for position directly above the fireplace. Such shelves are commonly used for locating television sets and decorative plants. Most direct vent fireplaces include tempered glass front doors. When these doors are closed even higher temperatures rising above the fireplace may result. These situations are not optimal to safely accept the elevated BTU's (e.g., 20,000–30,000 BTU) being vented into the room.
There are direct vent fireplaces that use downwardly facing vents at the outlet. See U.S. Pat. No. 4,793,322. However, even these do not prevent the rising heat from corrupting a mantel. Accordingly a need has occurred for providing greater heat deflection away from fireplace installations having a mantel.